1. Field of the Invention
The present invention relates generally to pumps and more specifically to a pump for implantation into the human body.
2. Description of the Prior Art
In the field of fluid delivery systems for use in the human body, the present devices are either not wholly implantable or the devices are not directly controllable or capable of preventing blow through caused by pressure applied to the inlet of the pump. The latter feature is necessary to insure that potentially dangerous overdoses of drugs or hormones are inadvertently forced into the host by sudden pressure on the reservoir, as might be caused by a blow. A miniature implantable roller type pump is described by G. D. Summers in "A New and Growing Family of Artificial Implanted Fluid Devices," Am. Soc. Art. Int. Organs 16: 219 (1970). This type of pump requires an extracorporeal power source which is supplied by an external motor magnetically coupled to the pump through the skin. Feedback control would require a rather complicated arrangement of the implanted and extracorporeal units. A fully implantable fluid delivery system is described by P. J. Blackshear et al., in "The Design and Initial Testing of an Implantable Infusion Pump," Surgery, Gynecology and Obstetrics 134: 51 (1972). It is powered by evaporation at a constant pressure of about 1/2 atmosphere of perfluoropentane isomers in an enclosed liquid-vapor system. A constant rate of outflow is maintained by a calibrated resistance in the outflow tube and by the viscosity of the delivered fluid. Feedback control in this system would require active valving of the outflow. But the lack of control over pumping pressure opens the possibility that the entire contents of the reservoir could empty into the host at a pressure of about 400mm Hg should the valve fail.
Both of the above described systems are capable of discrete quantitative delivery of aliquots of solution but each has serious drawbacks. There thus exists a need in the implantation field for a completely implantable fluid delivery system which is blow through proof, is susceptible to uncomplicated feedback control, is able to deliver discrete aliquots with reliability and requires sufficiently low power to permit a relatively long implantation life.